Tuning Supported Fe-Ag Catalysts for Selective Acetylene Hydrogenation: A Combined Experimental and Computational Study

The selective hydrogenation of acetylene is a key reaction step for purification in ethylene production, as trace amounts of acetylene can poison downstream polymerization catalysts. Industrial acetylene hydrogenation is currently performed almost exclusively using palladium-based catalysts, motivating the search for more abundant alternatives. In this study, supported Fe-Ag catalysts with different Fe:Ag ratios were synthesized and evaluated for the selective hydrogenation of acetylene under industrially relevant front-end conditions. The catalysts were characterized by XRD, N2-physisorption, TPR, XPS, STEM-EDX, ICP-OES and XRF, and density functional theory (DFT) calculations on idealized local Fe-Ag surface motifs were used to investigate composition-dependent trends in adsorption energetics. Catalyst characterization revealed no evidence for the formation of an extended Fe-Ag alloy phase after air exposure. Instead, Fe- and Ag-rich domains were found to coexist in close nanoscale proximity providing a structural basis for considering possible local Fe-Ag interactions. Accordingly, the DFT calculations were performed on idealized local Fe-Ag surface motifs to investigate how the local chemical environment around adsorption sites affects the adsorption energetics of reaction intermediates. DFT calculations predict a gradual weakening of adsorption strength with increasing local Ag content, while the experimental catalyst series independently shows a decrease in ethane selectivity with increasing Ag loading. Under CO-containing front-end conditions, catalyst selectivity increased further due to competitive adsorption effects, while the influence of catalyst composition became less pronounced. The combined experimental and computational results indicate that changes in the local Fe-Ag environment influence adsorption energetics and may contribute to the composition-dependent catalytic behavior in acetylene hydrogenation. These findings provide design principles for the development of palladium-free hydrogenation catalysts based on earth-abundant metals.